To go to multiprocessor, the Processors have to be the same size/speed/stepping. Look on top of your processor, it has a whitish grey stamp on top which should have the speed/size of cache/stepping on processor for example: 80523PY350512PE SL2U3
The 350 after the PY is my speed the 512 is my cache and the SL2 is my stepping on the processor. Make sure you have the same speed/cache and try to have a stepping that is only one number off or the same anything else won't work.
Now for the Processor Upgrade this is how to approach it: 1.Upgrade the system BIOS Firmware 2.Go to F10 and go to Advanced Modeby pressing(Ctrl+A) 3.Go to System Configuration>Configure HW>Review 4.Modify>View Edit details> 5.APIC Mode--Change this to Full Table. 6.Boot to NT and put in the Smart Start CD. Go to Multiprocessor HAL highlight and press upgrade and HAL recovery and press update. 7.When the install asks for the NT 4.0 CD don't put in the 8.CD but assign the directory with the expanded version of the service pack. Boot again and you should be OK.
Good Luck. If there are any further questions don't hesitate to ask.